Question

An indicator has a PK_a of 7.5 . What is the ratio of the concentration of base form to the concentration of acid form, in a buffer solution in which pH is 6.5?

Answer 1

The correct answer is 1/10.

Answer 2

 As we know,

\(pH = p{K_a}+ \log\frac{[salt]}{[acid]}\)

given,

\(pH \text{ & } pK_a = 7.5\)

\(\therefore 6.5 = 7.5 + \log\frac{[In^-]}{[HIn]}\)

⇒ \(\frac{[In^-]}{[HIn]} = 10^{-1} = \frac 1{10}\)